Immunoreactive glandular kallikrein levels in rat renal lymph, thoracic lymph and plasma are similar. In contrast, renin levels are 170-fold higher in renal lymph than in thoracic lymph while angiotension converting enzyme levels are 16% those of thoracic lymph. In keeping with the high renin and low converting enzyme activities, renal lymph contains high levels of angiotensin I. We conclude that, while renin is elaborated into the circulation by the kidney, there is no major passage of kallikrein from the tubular cells into the interstitium and the lymph. Binding of [3H]-bradykinin was studied in isolated segments of the rabbit nephron. Highest binding was observed in the cortical collecting tubule (CCT) and the outer medullary collecting tubule. Small but significant binding was also seen in the glomerulus, proximal straight tubule, cortical thick ascending limb of Henle's loop and distal convoluted tubule. Binding in the CCT was saturable and reached a plateau at 24 nM bradykinin, with half maximal binding at 12 nM. Scatchard analysis revealed a single binding component with a dissociation constant at 8.9 nM an a maximal number of binding sites of 6.8 x 10 to the -18 mol./mm. The binding data indicate that major sites of kinin action in the kidney are cortical and medullary collecting tubules. In preliminary studies net fluxes of Na and K in isolated rat collecting tubules were not observed in normal animals but after DOCA treatment the appropriate absorption of Na and secretion of K were observed.